1. Field of the Invention
The present invention relates to a disposition structure of a heat exchanger in a motorcycle, and more particularly to improvement technique on a disposition structure of a heat exchanger on a motorcycle, which has been considered from a point of view of improving cooling efficiency of the heat exchanger.
2. Description of Background Art
Conventionally, as disposition structure of the heat exchanger in a motorcycle, there is known structure in which a heat exchanger has been disposed forward of an internal combustion engine. Thus, this disposition structure of the heat exchanger is that it has been arranged in a substantially upright position to a vehicle advance direction.
Since, however, since an actual air flow passes through and between front forks and above the front wheel, and then goes toward the internal combustion engine (see, for example, Japanese Patent No. 3206151 (P.3, FIG. 1-2), and Japanese Utility Model Laid-Open No. Hei 1-176591), in such a disposition structure of the heat exchanger, an angle of incidence of the air flow to cooling fins of the heat exchanger becomes small so that no high cooling effect can be obtained. As a result, the maximum efficiency in the heat exchanger could not be brought about; however in order to secure sufficient cooling property in the internal combustion engine, it was necessary to make the heat exchanger larger sized. In the case of an air-cooled internal combustion engine, when there is the heat exchanger in front of the internal combustion engine, an air flow rate to be applied to the engine decreases, and when the heat exchanger is large, a problem in design cannot be ignored either.
In the invention described in Japanese Patent No. 3206151, shown in FIGS. 13(a) and 13(b), there has been described disposition structure of an oil cooler 01 in which a water-cooled engine 0E mounted on a motorcycle is described. An oil cooler 01 of this engine 0E is installed in the lower part, forward of the engine 0E below a radiator 02; and the oil cooler 01 is disposed with respect to the vehicle body with the slightly upper portion of a surface on which its multiplicity of cooling fins 011 stand in a row forward tilted. These cooling fins 011 extend in a direction orthogonal to the vehicle advance direction, and therefore, these cooling fins 011 are arranged with their fin surface at an angle substantially parallel with respect to the air flow.
Also, even in the invention described in Japanese Utility Model Laid-Open No. Hei 1-176591, shown in FIG. 14, as in the case of the invention described in Japanese Patent No. 3206151, there has been described structure, in which the oil cooler 01 is installed below the radiator 02 and in the lower part forward of the engine 0E close to the oil pan 03; and a surface on which its multiplicity of cooling fins stand in a row is actually placed in a state in which it is perpendicular or substantially perpendicular to the vehicle advance direction. Thus, these cooling fins extend in a direction orthogonal to the vehicle advance direction and the fin surface of the cooling fins is made horizontal or substantially horizontal to the air flow.
In the invention described in the above-described Japanese Patent No. 3206151 (P. 3, FIG. 1-2), and Japanese Utility Model Laid-Open No. Hei 1-176591, disposition of the oil cooler which is the heat exchanger in either case, has such a relationship that the cooling fins extend in a direction orthogonal to the air flow during vehicle driving; thus the cooling fins are arranged with their fin surfaces parallel to or substantially parallel to, or inclined by a predetermined acute angle to the air flow. Setting of this opposition relationship of these cooling fins with respect to the air flow is appreciated in its own way from points of view of formation of a smooth flow in the air flow and securing of predetermined heat exchange efficiency because the air flow flows between the cooling fins without meeting with any resistance comparatively.
Since, however, the air flow flows away so as to stroke the surface of the cooling fins, the formation of a smooth flow in the air flow is not capable of applying a sufficient amount of air flow to the cooling fins, nor is sufficient cold given to the fin surface of the cooling fins, and in the sense that the cold of the air flow is more effectively absorbed to make the best use in the cooling fins, any acceptable result is never given. There is, however, room for improvement from a point of view of further improving the heat exchange efficiency in the heat exchanger.
Also, according to the above-described disposition structure of heat exchanger, since a plane having large area on which a multiplicity of cooling fins of the heat exchanger stand in a row opposes an air flow so as to intercept at right angles or substantially at right angles, its projected area is large, and a flow of the air flow to be directly applied to the engine is significantly affected leading to the decreased running air flow rate to be directly applied to the engine.
Therefore, the above-described disposition structure of heat exchanger is not appreciated from a point of view of cooling of the engine in above all air-cooled internal combustion engine.
Under such circumstances as described above, it would be desirable to improve the structure by a comparatively simple change in structure for further improving heat exchange efficiency of the heat exchanger in a motorcycle.
Such an improved structure would dispose the heat exchanger on the motorcycle in a manner that would allow a sufficient supply of air flow to be supplied to the cooling fins during vehicle driving, thus bringing about the maximum heat exchange efficiency.